1. Field of the Invention
The present invention generally relates to a disk drive. More particularly, the invention relates to a method of perform servo writing for recording servo data on a disk-shaped medium.
2. Description of the Related Art
Most disk drives, a represented by hard disk drives, incorporate a servo system. The servo system controls the positioning of the head (magnetic head), or moves the head to a desired track on the disk-shaped medium, i.e., a data recording medium. The servo system controls the positioning of the head, by using the servo data recorded on the disk-shaped medium.
A method of manufacturing a disk drive includes a servo writing step, i.e., the step of recording servo data on the disk-shaped medium. A self-servo writing method is known, which is performed in the servo writing step. The self-servo writing method uses the head and actuator that are incorporated in the disk drive.
The disk drives developed in recent years incorporate a head that comprises a read-head element and a write-head element, both mounted on the same slider and separated from each other. The write-head element records data on a disk-shaped medium. The read-head element reads the data recorded on the disk-shaped medium. The read-head element has an MR (magnetoresistive) element in most cases.
The self-servo writing method uses the write-head element of the head incorporated in the disk drive, thereby writing servo data on the disk-shaped medium. The read-head element reads the servo data thus written on the disk-shaped medium.
In the servo writing step, it is necessary to write the servo data, precisely at a prescribed position on the disk-shaped medium. The head incorporated in the disk drive comprises two discrete elements, i.e., the read-head element and the write-head element. A position offset inevitably exists between these elements. The position offset corresponds to the distance between the centerlines of the read- and write-head elements. Hence, the head-positioning control must be carried out in the self-servo writing step, in accordance with the position offset between the read- and write-head elements.
More specifically, the position offset must be measured and the offset must be adjusted in accordance with the position offset measured, in order to control the positioning of the head. A method is proposed and developed, in which the position offset is measured by using a measuring pattern written on the disk shaped medium. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 8-129732.) This prior-art method uses a servo-burst pattern contained in the servo data, thereby to writing a measuring pattern on the disk-shaped medium. In this method, the measuring pattern is used, determining the distance between the centerline of the read-head element and one end of the write-head element and also the distance between the centerline and the other end of the write-head element. The distance from the centerline of the write-head element is obtained from the average of these distances determined. The position offset is thereby calculated.
Another prior-art method is proposed, which uses a servo-burst pattern to measures the position offset. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-334428.) In this method, the servo data for measuring the offset is written on the disk-shaped medium and the position error read from this servo data is applied as the position offset between the read- and write-head elements.
In short, the pattern for measuring the offset is merely a servo-burst pattern that is repeated, each time for one of the tracks provided on the disk-shaped medium. However, the position offset between the read- and write-head elements used in the disk drives developed in recent years amounts to several track intervals. This is because these disk drives record data on the disk-shaped medium at a high linear recording density.
With the conventional method using the measuring pattern that is only a servo-burst pattern, it is difficult to measure the position offset between the read- and write-head elements, directly and accurately. Unless the position offset is measured with high accuracy, no successful self-servo writing step can be carried out.
The conventional method using the measuring pattern that is only a servo-burst pattern can hardly measure the position offset between the read- and write-head elements, directly and accurately. It is therefore demanded that the position offset between the read- and write-head elements be measured with high precision to perform a successful self-servo writing step.